* Use golang.org/x/sys/unix for _linux.go sources
To support builds on GOARCH=386 and possibly elsewhere, it's necessary
to use the x/sys/unix package instead of the syscall package. This is
because the syscall package is frozen and does not support
SYS_GETSOCKNAME, SYS_RECVFROM, nor SYS_SENDTO for GOARCH=386.
This commit alone doesn't add support for 386 builds, just gets things
onto x/sys/unix so that it's possible.
The remaining uses of the syscall package relate to signals, which
cannot be switched to the x/sys/unix package at this time. Windows
support breaks, so they can either continue using the syscall package
(it's frozen, this is safe for Go 1.x at minimum), or something can be
written to just use both windows- and unix-compatible signals.
* Add linux-386, ppc64le targets to Makefile
Because 'linux' is linux-amd64 already, just add linux-386 and
linux-ppc64le targets to distinguish them. Would rename the linux
target but that might break existing uses.
Nate Brown